The present invention relates to a surface acoustic wave device, and in particular to an improvement in the sealing structure for the exciting portions and the propagating portion thereof.
Heretofore, in the case where a surface acoustic wave element is sealed while leaving a free space over the exciting portions and the propagating portion thereof, sealing structures indicated in FIGS. 14 and 15 are often used.
FIG. 14 shows a case where it is sealed in a metallic package, where reference numeral 1 is a surface acoustic wave element; 2 is the metallic package; 3 is an exciting transducer; 4 is an in- and output pin; 5 is a metallic cap; and 6 is conductive paste. The surface acoustic wave element 1 is mounted fixedly on a stem of the metallic package 2 by means of adhesive or the conductive paste 6. Each of a pair of exciting transducers 3 is connected electrically with an in- and output pin 4 of the package by wire bonding and the whole is sealed by covering it with the metallic cap 5 so that a free space is assured on the surface of the exciting portions and the propagating portion stated above.
FIG. 15 shows a case where it is sealed by resin mold, where reference numeral 7 is a surface acoustic wave element; 8 is a lead terminal; 9 is a resin mold; 10 is an air gap; and 11 is conductive paste. Each of electrodes on the surface of the element is connected with a lead terminal 8 by solder or the conductive paste 11. Before the step of sealing with mold resin 9 wax is applied to the surface of the exciting portions and the propagating portion so that the air gap 10 is formed at the same time as the formation of the resin mold.
However, for the sealing structure indicated in FIG. 14, since the metallic package is relatively expensive, it is difficult to lower the cost.
On the other hand, although the sealing structure indicated in FIG. 15 can be obtained with a low cost, it is feared that the surface of the surface acoustic wave element is polluted. Further, in the case where an air gap of large surface is required, it is difficult to apply wax uniformly thereto. Therefore, since fluctuations take place in the formation of the air gap, it has a drawback that the fabrication yield is lowered.